An image forming apparatus is an apparatus that is used to form an image on a paper or other printing medium according to one or more input signals. Examples of image forming apparatuses include printers, copiers, fax machines, and multi-functional peripheral devices that combine the functions of one or more of such apparatuses.
An example of an image forming apparatus is an electro-photographic image forming apparatus. In an electro-photographic image forming apparatus, an electrostatic latent image is formed on a surface of a photoreceptor by irradiating light on the surface of the photoreceptor that has been charged with a predetermined electric potential. A visible image can be formed by using a developing device that supplies a developer to the electrostatic latent image. The visible image formed on the photoreceptor can be directly transferred to, for example, a paper supplied by a paper supply unit through a transfer unit. The image transferred to the paper can be fixed on the paper by a fusing process. High capacity paper supply units have been developed and produced that include a first holding portion and a second holding portion such that papers in the second holding portion are fed to the first holding portion when the first holding portion is empty, such as when the papers loaded in the first holding portion have been depleted.